Collapse of quantized Hall plateaus in asymmetric double-quantum-well systems

The integer quantum Hall effect in asymmetric double-quantum-well structures is investigated for electron concentrations which are varied up to around the population threshold of the excited subband. The scattering time of electrons in the system is shown to be governed by the interface roughness. The ratio between the transport and single-particle scattering times is used to evaluate the fluctuations in the interface. We map out a phase diagram of spin-polarized and spin-unpolarized states. When the Fermi energy is raised to the bottom of the second subband, the resistance peak for the Landau level filling factor nu between 2 and 3 broadens and the nu = 3 Hall plateau collapses. The coupling of the Landau levels in the two quantum wells leads to an enhancement of the dissipative conductivity. The anomalous peak is found to exhibit nonlinear current-voltage characteristics.